1. Field of the Invention
The present invention generally relates to controlling the spacing of a tape head assembly (e.g., including one or more transducers such as a read transducer, a write transducer, or a read/write transducer) relative to a magnetic data storage tape and, more particularly, to controlling such spacing by reducing the buildup of tape stain on the tape head assembly over time.
2. Relevant Background
Tape drive manufacturers are constantly challenged to produce tape drives with larger storage capacity to meet market demands. One way to accomplish this objective is to increase the storage density in the magnetic layer of the tape. By increasing the storage density, the tape may have more tracks for a given area and each track may have more bits.
An important factor affecting the accuracy of the read/write processes and the ability to support higher data densities is magnetic spacing. Generally, magnetic spacing is the distance between the magnetic layer on the tape where the information is recorded and the transducer(s) write and read data. Magnetic spacing is a first-order effect in all magnetic recording systems because increased magnetic spacing degrades write performance (to store data) and read performance (retrieving data) alike. Furthermore, magnetic spacing is a critical parameter because the amplitude of a playback signal decreases exponentially with increasing magnetic spacing. The decrease in amplitude caused by increased magnetic spacing may be referred to as Wallace spacing loss. Increased magnetic spacing increases the width of the read back pulse which leads to reduced data densities. The quality of the write operation also varies with spacing and decreased magnetic spacing improves the quality of the write operation.
Magnetic spacing for a tape drive is typically set in the factory and can change during long term operation (e.g., long term movement of magnetic tape over the tape head assembly). After a sufficient period of time, a steady-state magnetic spacing develops. Magnetic spacing is generally designed to be in the range between 20-50 nm, depending upon product requirements. Generally, smaller magnetic spacing is capable of supporting higher data densities for a given read/write accuracy, while greater magnetic spacing is capable of supporting lower data densities for a given read/write accuracy. If a system is designed to run at high data densities, but the magnetic spacing is too large, an unacceptable drop in read/write accuracy will occur.
One factor that increases magnetic spacing (and thus can lead to read/write accuracy loss) is the accumulation of “tape stain” on the tape head assembly over time during operation of the tape drive. Tape stain formation is believed to be an electro-mechanical-chemical process in which an accumulation (e.g., amalgam) of lubrication products, head wear products, and other detritus produced from the head and tape (during the wear process that continues for the life of the tape drive) builds up on the tape head elements (e.g., shields, poles, substrates, reader elements, and/or the like), and can accumulate in differing amounts and at differing rates based on, among other factors, the particular environment in which the tape drive is operating (e.g., temperature, humidity, and/or the like). The accumulated tape stain increases the magnetic spacing between the head and the tape by physically pushing the tape further away from the head assembly. In some cases, tape stain can be electrically conductive which can cause shorts between film layers in the read transducer that are designed to be isolated and ultimately degrade read performance significantly. Regardless of whether or not it is electrically conductive, tape stain accumulated on the tape head assembly degrades overall performance and is a common cause for drive returns from customers.
One manner of reducing tape stain is via use of a “cleaning tape” having an abrasive surface that removes some of the stain. Upon accumulation of tape stain on a typical head assembly, drive software notes the performance degradation and requests that the tape library or tape operator loads the cleaning tape. In some situations, a cleaning tape can be periodically loaded even when performance degradation has not been noted. Although a common approach to mitigate the tape stain problem in the industry, use of cleaning tapes has significant disadvantages. For instance, use of cleaning tapes is often not completely effective in removing tape stain. Furthermore, cleaning tapes tend to decrease the overall mean time to failure of the head while increasing the cost of ownership of tape drives to customers. Still further, cleaning tapes merely mask the problem of tape stain accumulation by periodically and imperfectly removing the tape stain rather than eliminating or at least limiting the accumulation of the tape stain in the first place.